Track whether a keydown should perform text insertion separately from
the delivered code point. Native frontends and text-oriented test paths
can now mark events that came from text input, while shortcut-style key
events keep Alt-modified default insertion suppressed.
This lets macOS Option-generated text such as Option+A and Option+Space
insert into editable controls without making plain Alt shortcuts insert
their base character. Add coverage for Alt text, Ctrl+Alt text,
separator text, Ctrl-only shortcuts, and Alt shortcuts.
Seed the page background fallback from the platform color scheme before
WebContent has painted. Update the same fallback when the platform theme
changes, and when the preferred color scheme is forced through the debug
menu, so unpainted web view areas use the matching Canvas color.
Notify the UI process with the solid canvas background color recorded
for the top-level document. This is the Canvas system color with the
effective document background composited over it, matching the color
used before normal painting.
Store that color on the view and use it when AppKit, Qt, and Gtk need
to fill areas exposed while an older bitmap is still on screen during a
window resize.
